This invention relates to over-temp safety devices, and more particularly to an overtemp safety device that is not subject to circuit defaults, creep, or the usual inaccuracies associated with mechanical devices.
Over-temp devices are used in a number of different appliances. Almost every water heater has such a device. Almost every furnace has such a device. Additionally, almost every electrical appliance with heating elements therein has an over-temp safety device. It is therefore highly desirable to provide a new and improved over-temp safety device.
Some of the prior proposed over-temp safety devices utilize bi-metal controls such as the thermostats conventionally used with internal combustion engines. These bi-metal controls not only are inaccurate, but age over time to become totally inoperable. It is therefore highly desirable to provide a new and improved over-temp safety device that does not age or become inoperative over time at temperatures below the desired temperature (hereinafter xe2x80x9ccritical temperaturexe2x80x9d) above which operating temperatures should not exceed.
Fusible metal devices have also been widely used. Fusible metal solder elements have been utilized as part of an electrical circuit as a safety device. The circuit opens when the fusible metal melts at the critical temperature. However, fusible metal has been well known to lose its adhesion properties with other metals and therefore, at times, these circuits will open when not intended.
Fusible metal links many times are spring loaded or weight loaded to ensure that the fusible metal link fails when the critical temperature is reached. However, fusible metal is also known to creep at temperatures less than the desired temperature and thus fail when not intended.
Further, when fusible metal elements are part of an electrical circuit, at times, the heat generated by electrical current passing through the fusible metal will cause the device to fail, not because the device has been presented with a temperature above the critical temperature, but only because of the current and resistance of the device has heated the device.
Still further, when a fusible device is part of circuit, in order for the fusible device to work as intended, it must not only release, but disconnect. In some structures the device has released, but because of where the melted metal flows, the electrical circuit has not disconnected.
Thus, it is therefore highly desirable to provide a new and improved over-temp safety device that both releases as intended and also disconnects. It is also highly desirable to provide a new and improved over-temp safety device that will not creep and fail at temperatures below the critical temperature. It is also highly desirable to provide a new and improved over-temp safety device that is not part of an electrical circuit. It is also highly desirable to provide a new and improved over-temp safety device that is not dependent upon the adherence of fusible metal or the physical properties of the fusible metal or its electrical conductivity or resistance.
Solid state electronic devices such as thermistors have also been used in overload devices. However, these devices are also subject to failure over time in the presence of temperatures lower than the critical temperature or aging. It is therefore highly desirable to provide a new and improved over-temp safety device that does not utilize solid state electronic devices. It is also highly desirable to provide a new and improved over-temp safety device that is totally mechanical in nature. It is also highly desirable to provide a new and improved over-temp safety device that does not age.
It is the intent of all temperature overload devices to be totally impartial to how heat is applied to the device, i.e. whether by conductance or radiation or a combination of the same and both the frequency and range of the oscillation of the temperature of the device during use. One of the reasons why fusible metal devices are widely used is the well known property of fusible metals to melt at a constant temperature. Thus, by utilizing the critical melt temperature of the device, that temperature must first be reached, and second be maintained sufficiently long enough for the device to melt. It is the intent of all who use fusible devices that the device trip as soon as the temperature is reached; and thus, fusible metal devices usually utilize small amounts of fusible metal and highly conductive supporting structures such that as soon as the temperature is released, the metal melts and the device trips. Thus, all fusible metal devices are designed such that once the critical temperature is reached; there are no mechanical structures that will prevent the fusible device from releasing and/or disconnecting. It is therefore highly desirable to provide a new and improved over-temp safety device that uses a fusible metal trigger that is not under stress, or, if under stress is supported so as to not subject the fusible metal to creep at temperatures below the critical temperature. It is therefore highly desirable to provide a new and improved over-temp safety device that uses a fusible metal trigger that is either not under stress, or, if under stress is supported so as to not subject the fusible metal to creep at temperatures below the critical temperature and that is impartial to how the heat is applied to the device. It is therefore highly desirable to provide a new and improved over-temp safety device that uses a fusible metal trigger that is either not under stress, or, if under stress the metal is supported so as to not subject the fusible metal to creep at temperatures below the critical temperature that is impartial to how the heat is applied to the device and that is impartial to the rate at which the temperature is applied to the fusible metal. It is therefore highly desirable to provide a new and improved over-temp safety device that uses a fusible metal trigger that is either not under stress, or, if under stress the metal is supported so as to not subject the fusible metal to creep at temperatures below the critical temperature that is impartial to how the heat is applied to the device and that is impartial to the rate at which the temperature is applied to the fusible metal and that releases and disconnects immediately upon the critical temperature being reached even when used at temperatures below the critical temperature for long periods of time.
Finally, it is highly desirable to provide a new and improved over-temp safety device that has all of the above features.
It is therefore an object of the invention to provide a new and improved over-temp safety device.
It is also an object of the invention to provide a new and improved over-temp safety device that does not age or become inoperative over time at temperatures below the critical temperature above which operating temperatures should not exceed.
It is also an object of the invention to provide a new and improved over-temp safety device that both releases as intended and also disconnects.
It is also an object of the invention to provide a new and improved over-temp safety device that will not creep and fail at temperatures below the critical temperature.
It is also an object of the invention to provide a new and improved over-temp safety device that is not part of an electrical circuit.
It is also an object of the invention to provide a new and improved over-temp safety device that is not dependent upon the adherence of fusible metal or the physical properties of the fusible metal or its electrical conductivity or resistance.
It is also an object of the invention to provide a new and improved over-temp safety device that does not utilize solid state electronic devices.
It is also an object of the invention to provide a new and improved over-temp safety device that is totally mechanical in nature.
It is also an object of the invention to provide a new and improved over-temp safety device that does not age.
It is also an object of the invention to provide a new and improved over-temp safety device that uses a fusible metal trigger that is not under stress, or, if under stress is supported so as to not subject the fusible metal to creep at temperatures below the critical temperature.
It is also an object of the invention to provide a new and improved over-temp safety device that uses a fusible metal trigger that is either not under stress, or, if under stress is supported so as to not subject the fusible metal to creep at temperatures below the critical temperature that is impartial to how the heat is applied to the device.
It is also an object of the invention to provide a new and improved over-temp safety device that uses a fusible metal trigger that is either not under stress, or, if under stress the metal is supported so as to not subject the fusible metal to creep at temperatures below the critical temperature that is impartial to how the heat is applied to the device and that is impartial to the rate at which the temperature is applied to the fusible metal.
It is also an object of the invention to provide a new and improved over-temp safety device that uses a fusible metal trigger that is either not under stress, or, if under stress the metal is supported so as to not subject the fusible metal to creep at temperatures below the critical temperature that is impartial to how the heat is applied to the device and that is impartial to the rate at which the temperature is applied to the fusible metal and that releases and disconnects immediately upon the critical temperature being reached but not before without aging.
It is finally an object of the invention to provide a new and improved over-temp safety device that has all of the above features.
In the broader aspects of the invention there is provided a new and improved over-temperature control device comprising a heat conductive surface, the temperature of which to be controlled below a selected critical temperature. A slug of fusible material at the critical temperature is positioned on the heat conductive surface. The slug has a hole therein and a headed bolt in the hole. The hole is less than the dimensions of the bolt head whereby the head cannot pass through the hole of the slug. A plate overlays the heat conductive surface with the slug therebetween. The plate has a hole therein through which the bolt head may pass. The plate hole and bolt and slug hole are coaxial. A compression spring urges the plate and the conductive surface together with the slug therebetween with less pressure than required to cause the fusible material of the slug to flow at temperatures below the critical temperature. The bolt is connected to a normally open switch by a spring in tension urging the bolt to pass through the holes in the plate and slug, and holds the switch in a closed condition with less force than required to overcome the compression spring and to separate the plate from the head conductive surface and less force than required to pull the bolt head through the hole in the slug in a non-melted condition. The spring in tension is released from tension and opens the switch when the bolt head is allowed to move through the hole of the slug and plate by the melting of the slug.